Although the advent of recombinant DNA technology has resulted in a rapidly expanding list of peptide-based drugs, a major drawback of peptide-based therapy has acutely hampered realization of the full potential of this field: in general, peptide-based drugs cannot be orally administered in effective doses, since they are rapidly degraded by enzymes in the gastrointestinal tract before they can reach the bloodstream. Unless the polypeptide of interest can be altered to make it relatively resistant to such enzymes, the only practical method of delivering the drug is likely to be a parenteral route, such as by intravenous, intramuscular, or subcutaneous injection. Administration by other parenteral routes (e.g., by absorption across nasal, buccal or rectal membranes, or via the lung) has met with limited success.
It has been found that when a peptide or protein (hereinafter collectively referred to as a polypeptide) is combined with an appropriate absorption enhancer and is introduced into the lung in the form of a powder of appropriate particle size, it readily enters the pulmonary circulation by absorption through the layer of epithelial cells in the lower respiratory tract. This is conveniently accomplished by inhalation of the powder from an inhaler device which dispenses the correct dose of powdered polypeptide/enhancer in a particle size which maximizes deposition in the lower respiratory tract, as opposed to the mouth and throat. (For ease of reference, the polypeptide and enhancer are hereinafter collectively referred to as the xe2x80x9cactive compoundsxe2x80x9d). To accomplish this preferential delivery into the lung, as much as possible of the active compounds should consist of particles having a diameter less than approximately 10 xcexcm (e.g., between 0.01-10 xcexcm, and ideally between 1-6 xcexcm). In preferred embodiments, at least 50% (preferably at least 60%, more preferably at least 70%, still more preferably at least 80%, and most preferably at least 90%) of the total mass of active compounds which exits the inhaler device consists of particles within the desired diameter range.
The invention thus includes a pharmaceutical composition containing a mixture of active compounds (A) a pharmaceutically active polypeptide and (B) an enhancer compound which enhances the systemic absorption of the polypeptide in the lower respiratory system (preferably the lungs) of a patient, the mixture being in the form of a dry powder suitable for inhalation, in which at least 50% of the total mass of active compounds (A) and (B) consists of primary particles having a diameter less than or equal to about 10 microns. The primary particles may be packaged as such, or may optionally be formed into agglomerates, which then are substantially deagglomerated prior to entry into the respiratory tract of the patient. The composition may of course contain other ingredients as needed, including other pharmaceutically active agents, other enhancers, and pharmacologically acceptable excipients such as diluents or carriers. Therefore, the therapeutic preparation of the present invention may contain only the active compounds or it may contain other substances, such as a pharmaceutically acceptable carrier. This carrier may largely consist of particles having a diameter of less than about 10 microns so that at least 50% of the resultant powder as a whole consists of optionally agglomerated primary particles having a diameter of less than about 10 microns; alternatively, the carrier may largely consist of much bigger particles (xe2x80x9ccoarse particlesxe2x80x9d), so that an xe2x80x9cordered mixturexe2x80x9d may be formed between the active compounds and the said carrier. In an ordered mixture, alternatively known as an interactive or adhesive mixture, fine drug particles (in this invention, the active compounds) are fairly evenly distributed over the surface of coarse excipient particles (in this invention, the pharmaceutically acceptable carrier). Preferably, the active compounds are not in the form of agglomerates prior to formation of the ordered mixture. The coarse particles may have a diameter of over 20 microns, such as over 60 microns. Above these lower limits, the diameter of the coarse particles is not of critical importance, so various coarse particle sizes may be used, if desired, according to the practical requirements of the particular formulation. There is no requirement for the coarse particles in the ordered mixture to be of the same size, but the coarse particles may advantageously be of similar size within the ordered mixture. Preferably, the coarse particles have a diameter of 60-800 microns.
The polypeptide may be any medically or diagnostically useful peptide or protein of small to medium size, i.e. up to about 40 kD molecular weight (MW), for which systemic delivery is desired. The mechanisms of improved polypeptide absorption according to the present invention are generally applicable and should apply to all such polypeptides, although the degree to which their absorption is improved may vary according to the MW and the physico-chemical properties of the polypeptide, and the particular enhancer used. It is expected that polypeptides having a molecular weight of up to 30 kD will be most useful in the present invention, such as polypeptides having a molecular weight of up to 25 kD or up to 20 kD, and especially up to 15 kD or up to 10 kD. Any desired polypeptide may be easily tested for use in the present invention with a particular enhancer, by in vivo or in vitro assays, as described herein.
The enhancer compound used in the compositions of the present invention can be any compound which enhances the absorption of the polypeptide through the epithelium of the lower respiratory tract, and into the systemic circulation. By xe2x80x9cenhances absorptionxe2x80x9d is meant that the amount of polypeptide absorbed into the systemic circulation in the presence of enhancer is higher than in the absence of enhancer. Preferably the amount of polypeptide absorbed is significantly higher (p less than 0.05) in the presence of enhancer. The suitability of any potential enhancer for use in the present invention may be easily assessed, by means of in vivo or in vitro assays, as described herein.
The amount of polypeptide absorbed according to the present invention is preferably at least 150% of the amount absorbed in the absence of enhancer. In preferred embodiments, absorption of polypeptide is at least doubled, more preferably tripled, and most preferably quadrupled in the presence of the enhancer, compared to in its absence.
The enhancer is preferably a surfactant such as a salt of a fatty acid, a bile salt, a bile salt derivative, an alkyl glycoside, a cyclodextrin, or a phospholipid. The enhancer may be, for example, a sodium, potassium, or organic amine (e.g., lysine) salt of the fatty acid, and the fatty acid is preferably capric acid or another fatty acid of 8-16 carbon atoms. The preferred enhancer is sodium caprate. The ratio of polypeptide to enhancer will preferably vary from about 9:1 to about 1:1. Although proportions of enhancer greater than 1:1 would presumably enhance uptake as well as or better than lower proportions, it is believed that the amount of enhancer used should be no higher than necessary to acheive the desired level of enhancement, since excess enhancer may trigger unwanted side effects, such as local irritation.
Also within the invention is a method of administering systemically a pharmaceutically active polypeptide, by causing a patient to inhale the pharmaceutical composition of the invention, wherein at least 50% of the total mass of the active compounds at the point of entry to the respiratory tract of the patient consists of particles having a diameter less than or equal to about 10 microns. This is preferably accomplished by the use of an inhaler device from which the patient inhales the powder. Where the powdered composition is in the form of agglomerates of primary particles, the device is preferably configured to induce substantial deagglomeration of the agglomerates upon inhalation of the powder from the device by the patient, so that the majority of the agglomerates break down into particles having a diameter less than or equal to about 10 microns, prior to entry of the powder into the respiratory system of the patient. This deagglomeration would occur inside the device, and is typically induced by the air turbulence created in the device by the force of inhalation. Agglomerates are in general preferably not formed in the ordered mixture. In the case of an ordered mixture, the active compounds should be released from the large particles preferably upon inhalation, either by mechanical means in the inhaler device or simply by the action of inhalation, or by other means, the active compounds then being deposited in the lower respiratory tract and the carrier particles in the mouth.
The inhaler device is preferably a single dose dry powder inhaler, but may alternatively be a multi dose dry powder inhaler.
The invention also includes processes for the manufacture of a pharmaceutical composition suitable for administration by inhalation. In one such process, a solution is first provided in which are dissolved (a) a pharmaceutically active polypeptide and (b) an enhancer compound which enhances the systemic absorption of the polypeptide in the lower respiratory tract of a patient. The solvent is then removed from the solution to yield a dry solid containing the polypeptide and the enhancer, and the dry solid is pulverized to produce a powder. A second such process involves dry mixing (a) a pharmaceutically active polypeptide and (b) an enhancer compound, and micronizing the obtained mixture. Yet a third suitable process includes the steps of providing a first micronized preparation containing a polypeptide and a second micronized preparation containing an enhancer compound, and mixing the two micronized preparations together. When a carrier is to be included other than when an ordered mixture is desired, this may be added to the solution, or to the dry-mixture of the pharmaceutically active polypeptide prior to micronization, or micronised carrier may be dry mixed with the other micronised components. In producing an ordered mixture, micronised polypeptide and enhancer are mixed with a suitable carrier.